1. Field of the Invention
The present invention pertains to the field of electrical communications, more particularly the field of continuous variable indication or telemetering, and to the field of electrical computers and data processing systems, more particularly the field of measuring, or monitoring systems having programmed testing conditions.
2. Description of the Related Art
In a conventional telemetry system, serial digital data, which represents periodically sampled measurements of a number of parameters or variables being measured during a test, is received on a carrier frequency in successive, synchronous frames. Typically, the data is displayed in real time on strip chart recorders. Usually different subjects, such as different aircraft, are involved in a testing project. Each subject typically has a different telemetry frequency, and the subjects may use different forms of modulation and multiplexing. Each frame has a synchronization word followed by a predetermined number of data words which may be arranged in a predetermined sequence of the parameters with each word representing one sample of one of the parameters. However, in "supercommutation" several words in a frame may represent the same parameter and in "subcommutation" the same word position in successive frames may represent different parameters. Data for several parameters may be packed in one word. Individual bits in a word may each represent a "discrete" parameter, and several such bits may be displayed as a single parameter. Data from several telemetry frequencies may be directed to the same display. Each frame is "decommutated" into successive parallel data words corresponding to the data words of the frame and is accompanied by strobe signals identifying the presence of a frame and each word.
Conventionally, a demultiplexer, which typically includes several digital to analog converters (DAC's) each driving a pen of a strip chart recorder, directs the successive parallel words corresponding to a selected parameter to a predetermined one of the DAC's. The direction of parameters to particular DAC's is determined by patch panel wiring which selects the proper data words by their position in their respective frames. For scaling and number conversion, a conventional demultiplexer has patch panel wiring allowing any bit of a parallel data word to be directed to any input bit of a DAC. Such a patch panel provides for changing the DAC receiving a parameter and for changing the scaling of a parameter while data is being received without affecting the display and recording of data for any other parameter. Since patch panel wiring is complex and error prone, it is usual to maintain a "library" of wired patch panels for parameters common to different projects; however, the cost and space of such a library is highly disadvantageous.
Such a conventional telemetry system does not have the ability to handle later developments in telemetry formats. For example, the location of parameters within a frame may be more complex than in supercommutation and subcommutation as described above. Also, data for a set of parameters may be received asynchronously and be identified by predetermined identifier word appearing in a frame having data for the set.
As a result, telemetry preprocessors have been developed to sort out and scale data received from various sources and received at irregular intervals. As data is received at rates of up to several million words per second, a preprocessor sorts out each parameter and outputs, asynchronously and in parallel format, a word with the corresponding data together with a tag word identifying the data and with a strobe signal. The output data word identified by a tag word may be packed with multiple bit or discrete data representing several parameters. A telemetry preprocessor includes several digital processors and controllers having stored tables which are programmed by a separate, host computer and which control the sorting and scaling of input data and specify the tags and destinations of output data for display. Typically, each class of subjects involved in a telemetered test project uses similar such tables so that the tables for decommutation and demultiplexing the input data of a telemetry project may be largely programmed from existing tables. However, the tables related to the output data must be arranged for the parameters of interest in a particular project. Although the preprocessor tables provide great flexibility in parameter selection and are easily stored, these tables are so complex that they cannot be easily changed to vary the tags, scaling, and data destination. In any event, several minutes are required to load the preprocessor tables from a host computer, and data cannot be displayed during table loading. As a result, desirable changes in parameter selection, scaling, and display destination are not practical during a test using a telemetry preprocessor.
The present applicant's United States Statutory Invention Registration (SIR) H241 published Mar. 3, 1987 discloses a telemetry word selector used with a data compressor which, like an above-described preprocessor, receives telemetry data from several decommutators, sorts out parameters, and asynchronously and sequentially outputs parallel data words each with a tag word identifying the source of the data. Such a compressor is also like a preprocessor in requiring complex programming and being unsuited to changes during a test. The selector of SIR H241 has eight DAC's corresponding to the usual number of pens in a strip chart recorder. This selector has a memory storing tags and scaling codes individually associated with the DAC's, and each DAC and the corresponding tag are addressed by the same address counter. As this selector receives each tag word, the address counter is initiated to scan the memory for a matching tag. If a match is found, the data word, after scaling, shifting, and conversion controlled by the corresponding code, is directed to the DAC addressed by the counter. It is evident that this selector cannot direct one or more parameters in a data word to different DAC's. This selector has a panel with a display and a keyboard for entering the tags and conversion codes for several telemetry projects.
It is usual to record serial telemetry data for later analysis where parameters can be unpacked, scaled, and otherwise manipulated. However, this is irrelevant during a test where telemetered data must be observable to detect events requiring changes in the operation of subjects involved in the test; to better display parameters which become of particular interest; to combine displays of parameters; and to correct the display of parameters which are improperly scaled, directed, or unpacked.
These complexities exist because heretofore each received sample of every parameter was not simply "broadcast" with a tag--which typically need not be changed between projects--for different projects by assigning DAC's to receive suitably unpacked and scaled data selected by tag and by using arrangements that allow altering DAC selection and scaling for any parameter during a test without affecting data display for other parameters.